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IBM Personal Computer 340 CPU Issues

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    IBM Personal Computer 340 CPU Issues

    Hello, I have the following IBM Personal Computer 340 I am currently restoring/upgrading:

    Machine Type: 6560-17A
    Surepath BIOS Flash Revision Level LXKT20AUS
    BIOS Date: 07/21/96
    System Board Identifier: 0YVTGL28S25

    I'm trying to replace the original Intel Pentium 100 CPU with an Intel Pentium 200 CPU (non-MMX of course).

    - The FSB jumpers can be set for 50MHz, 60MHZ, or 66MHz
    --- I set them for 66MHZ

    - The multiplier jumpers can be set for 1.5x, 2.0x, 2.5x, and 3.0x
    --- I set them for 3.0x

    - The CPU voltage jumper can be set for 3.3V or 3.52V
    --- I set it for 3.3V

    When I install the 200MHz CPU it is still reported at 100MHz? I played the binary shuffle with the multipliers but that only resulted in the CPU being reported as 0MHz at times or 100MHz, nothing else.

    I installed an Intel Pentium 133MHz CPU (66MHZ FSB, 2.0x) and that works fine. I don't currently have a 166MHz CPU laying around to test.

    I don't understand why 66MHz with a multiplier of 3.0x is not working? I looked around for BIOS updates but these seem non-existent (I would much appreciate if someone could point me to a location to find IBM BIOS updates).

    Is there something I'm missing with this model/series of IBM systems?

    Any help would be appreciated. Thank you.

    If the motherboard can't properly determine the CPU speed at 200 MHz, it very likely doesn't support it.

    Many motherboard vendors in the 1990s often included bus speeds and multipliers that didn't actually work. They were usually intended for forwards compatibility with not yet released processors, but in many cases never actually worked due to bugs in the board, chipset limitations or never getting a newer BIOS release.

    Sometimes you can get lucky though, and the CPU will still operate at the proper speed, despite the BIOS not being able to report the speed properly.

    Try this program in DOS:


      I'll see what System Speed Test reports, thank you. As you pointed out I figured the limitation falls somewhere in either the motherboard or BIOS. I'm hoping that someone has successfully upgraded the model 340 beyond 133MHz and can help point me in the right direction. I've seen YouTube video of people getting their 340 systems working with a 166MHz CPU, so there's a chance 200MHz will work as well. Thank you for the reply.


        Most likely just a display anomaly since the BIOS lacks an entry for that CPU. If you set it to 66 x 3.0, it will run at 200 MHz, as the multiplier pins are a direct connection to the socket 7 and the BIOS has no control over the actual speed of the CPU.


          Originally posted by Timo W. View Post
          Most likely just a display anomaly since the BIOS lacks an entry for that CPU. If you set it to 66 x 3.0, it will run at 200 MHz, as the multiplier pins are a direct connection to the socket 7 and the BIOS has no control over the actual speed of the CPU.

          I had to upgrade the BIOS which I found here:

          After *finally* finding the BIOS updates I noticed a later BIOS than mine supported up to 166MHz CPUs. I flashed the BIOS with the latest revision, set the jumpers for 166MHz and it actually reported that in BIOS using a 200MHz CPU.

          Per Timo W.'s suggestion I set the speed for 200MHz and sure enough, SPEEDSYS reports the system running at 200MHz even though the BIOS reports a 100MHz CPU.

          (Thanks to GiGaBiTe for the SPEEDSYS link)

          What a HUGE improvement in performance! I upgraded the video RAM to 2MB as well. This thing chews through DOS games almost as well as a 233MMX system would.

          Now a new anomaly to deal with: When I upgraded the video RAM to 2MB the mouse pointer in Windows for Workgroups 3.11 turned into a splotchy looking square, LOL. This is probably because I am using the Cirrus Logic Alpine drivers meant for the GD5430 chipset. This system has the CL 5434 chipset so I'll need to find either an exact match or something closer than the Alpine drivers.


            Correction, that's a GD5436 video chipset contained in this PC. As I suspected, the correct video drivers fixed the funky mouse image.

            I found the IBM Windows 3.1x video drivers here:


            Other IBM video drivers pertaining to this computer can be found here:


            Duke Nukem 3D and Quake/Quake II run as smooth as silk on this system with a 200MHz CPU installed. Very happy with the results.

            Thanks for the help everyone


              Nice to hear. One of my retro systems is a 200 MHz Pentium system as well and I'm loving it.